SINOPSIS

Laminar natural convection heat transfer from a horizontal isothermal cylinder immersed in a Bingham fluid situated above or below an adiabatic wall has been studied over ranges of parameters, Rayleigh numbers (10 ≤ Ra ≤ 10⁵), Prandtl numbers (10 ≤ Pr ≤ 100), and Bingham numbers (0.1 ≤ Bn ≤ 10³) for cylinder-to-wall gaps |H/D| = 0.05, 0.1, 0.3, 0.7, 1.1, and 1.5. Detailed flow and temperature fields are analyzed in terms of the streamlines, isotherms, and the yield surfaces. At the next level, these results are discussed in terms of the local and average Nusselt number. For sufficiently large values of the Bingham number, the average Nusselt number reaches its asymptotic value commensurate with the conduction limit. The average Nusselt number increases with the Rayleigh number and |H/D|, while the Bingham number has an adverse influence with reference to the behavior in Newtonian fluids otherwise under identical conditions. The limiting value of the Bingham number (Bn_max) increases with the increasing Rayleigh number. With reference to the case of an unconfined cylinder, the confining adiabatic wall has an adverse influence on the overall heat transfer. Simple predictive expressions are developed which can be used to estimate the values of the average Nusselt number and the limiting Bingham number in a new application.